1. Field of the Invention
The present invention relates to conductive probe microscopes, and more particularly to atomic force microscopes.
2. Description of the Related Art
Scanning probe microscopy, such as conductive atomic force microscopy (CAFM), is widely used for observing and analyzing sample surfaces in the atomic scale. One conventional example of an atomic force microscope (AFM) uses a probe that has a microfabricated tip mounted on a flexible cantilever. The tip is typically made from Si3N4 or Si. The tip is slowly scanned across the surface of a material, just a few angstroms away from the surface (non-contact mode) or in contact with it (contact mode). The force between the atoms on the surface of the material and those on the tip cause the tip to deflect. The magnitude of the deflection depends on the separation between the surface atoms and the tip atoms and on the atomic forces between them, such as van der Waals forces or Pauli exclusion forces. This deflection can be recorded in various ways, the most common of which uses a laser focused on the top of the cantilever and reflected onto photodetectors. The photodetector signals are used to map the surface topography of samples with resolutions down to the atomic and nano scales. The lateral and vertical movements of the tip or sample are controlled by piezoelectric transducers and a feedback loop that produce voltage differences proportional to the movement.
After mapping a microscopic feature of interest, such as a sub-micron magnetic tunnel junction, the conductive tip can be used to make an electrical measurement of the feature. The tip is centered over the feature and then the x-y scanning is stopped. The tip is then lowered into contact with the feature. After contact is made, current can be passed through the feature to make an electrical measurement.
During the process of lowering the tip into contact with the feature, the tip usually must be pushed onto the sample surface progressively harder until electrical contact is made. This causes the tip to wear out rapidly, usually after only a few contacts. Further, the downward force on the tip required to maintain electrical contact between the tip and the sample surface can damage the sample.